An air pump is disclosed in EPA 0 385 298 Al, which has the disadvantage of producing vibrations which are transferred to the pump support or the apparatus receiving the secondary air to create high frequency noise during use because of an unequal distribution of mass in the pump impeller and in the electric motor and the magnetic rotary field which arises.
Recently, noise from the drive means of motor vehicles has been reduced considerably whereby any noise from the air pump becomes audible in the passenger compartment of the vehicle and this is undesirable.
In order to reduce this noise, DE-A1 41 07 049.6 proposes that the electric motor be supported by means of two elastic supports placed between the electric motor and the housing.
Although these means lead to a significant reduction in noise, irregularly occurring rattling noises are nevertheless produced during particular phases of operation due to the fact that an inlet collar located on the impeller, and projecting over an air inlet support, impacts against the supports, which are securely attached to the pump housing, especially during extended low frequency rotation with a large amplitude.